Stepping motor

ABSTRACT

In a stepping motor in which a cylindrical magnet  3  which is magnetized in an axial direction is coupled with a rotary shaft and said magnet is clamped with rotor stacks  4, 5  formed by laminating annular magnetic plates the surfaces of which are electrically insulated to form a rotor, and around the outer circumference of the rotor stator cores which are wound with stator coil are disposed, a sleeve  15  is pressed in between the magnet  3  and the rotor stacks  4, 5 , and the rotary shaft and interposed therebetween. The cutting operation for the outer diameter during the manufacturing processes is carried out while holding both ends of the sleeve  15 , subsequently the rotary shaft is inserted, thereby, regardless of the length of the rotary shaft, the manufacturing processes are carried out to reduce the number of the molds.

This is a Division of Application Ser. No. 09/310,353 filed May 12, 1999now abandon. The entire disclosure of the prior application(s) is herebyincorporated by reference herein in its entirety.

BACKGROUND OF THE INVENTION

1. Field of Invention

The present invention relates to an improvement of a stepping motor, inparticular, a rotor of it which is called as a hybrid type.

2. Background of Related Art

The structure of a stepping motor of this kind is explained referring toFIG. 3. On a rotor shaft 2, a magnet 3 magnetized in an axial directionis fixed by being inserted by the rotor shaft 2 in a hole 3 a, and bothsurfaces of which are clamped with a rotor stacks 4, 5 formed by beinglaminated with annular magnetic plates (silicon steel) surfaces of whichare electrically insulated, thereby, a rotor 6 is formed. The rotorstacks 4, 5 are also inserted by the rotor shaft 2 through holes 4 a, 5a provided in the center thereof.

The rotor shaft 2 of the rotor 6 is supported rotatably on casings 9, 10by bearings 7, 8. And, at the outer circumference side of the rotor 6, astator core 12 wound with a stator coil 11 is disposed, which is clampedwith the casings 9, 10.

FIG. 4 is a plan view where the rotor 6 is inserted in the stator coil11 and FIG. 5 is a perspective view of the stator core 12. The statorcore 12 is approximately square in its outer configuration, and at acenter opening thereof a plurality of projection poles 12 a directedtoward the center respectively. Around the projection poles 12 a thestator coil 11 is wound. This stator core 12 formed with a plurality ofmagnetic plates laminated. These magnetic plates laminated are connectedby being inserted with bolts not shown through the holes 12 b providedat their 4 comers.

As shown in FIG. 4, on the projection pole 12 a, a plurality of minutepole teeth 12 c are. provided, and on the rotor stacks 4, 5 of the rotor6 too, a plurality of pole teeth 3 a are provided opposing the poleteeth 12 c. The spacing between these pole teeth 12 c and 3 a is minutein dimension of less than 30 μm. Since at this minute spacing the rotor6 rotates, normally it has been necessary to be worked by cutting theouter diameter of the rotor 6 after being assembled. That is, accordingto the conventional manufacturing process of the rotor 6, the rotor 6has been assembled in such a manner as the rotor stacks 4, 5 which areformed by being laminated with the electrically insulated magneticplates (silicon steel plates) and the magnet 3 which is a component ofthe rotor 6 are assembled on the rotor shaft 2 simultaneously by theprocesses of press-in and gluing to obtain the rotor 6 as shown in FIG.6.

On both ends of the rotor shaft 2, central holes (not shown) areprovided in their axial directions, and, the outer diameter cutting hasbeen carried out by the following processes in such a manner, as shownin FIG. 7, the concentricity is secured by being inserted with thecenter hole holding apparatus 13 of the outer diameter cutting machineand touched in its outer diameter with a grinding stone 14 for use ofouter diameter cutting.

In a conventional manufacturing method of the rotor, the rotor stacksand the magnet as components of the rotor are pressed in and glued onthe rotary shaft simultaneously. However, since the length of eachrotary shaft is different respectively in accordance with its use of thestepping motor, even if the rotor stacks and the magnet are common, amanufacturing lot controlling as a rotor can not arranged, so that theproduction of the rotor has been carried out per every lot of variouskind of rotors.

In the case where the rotor stack, the magnet and the rotary shaft aremolded in a unit, since the length of the rotary shafts is different,there have needed various kind of molds and have been difficulties inboth of manufacturing of the rotor and managing of the molds. Further,when using a magnetic material as the rotary shaft, in the case wherethe rotor stacks are mounted directly on the rotary shaft, the leakageof the magnetic bundle of the magnet occurs through the N-pole of themagnet, one rotor stack, the rotary shaft, the other rotor stack and theS-pole of the magnet, a non-magnetic material had to be used as therotary shaft. Therefore, there have been remained some anxieties for therotation precision and the durability.

The present invention is to provide a stepping motor in which suchproblems as mentioned above in the conventional stepping motor areimproved.

SUMMARY OF THE INVENTION

The present invention is, according to a first aspect of the presentinvention, characterized in that, in a stepping motor in which a magnetwhich is a cylindrical and magnetized in its axial direction is coupledon a rotary shaft, both surfaces of which are clamped with rotor stacksformed by laminating annular magnetic plates the surface of which iselectrically insulated to form a rotor and a stator core around of whicha stator coil is wound is disposed around the outer circumference of therotor, between the rotary shaft, and the magnet and the rotor stacks anon-magnetic sleeve is interposed.

Further, according to a second aspect of the present invention, thelength of the sleeve in the first aspect described above is projectedaxially out of the rotor stacks disposed on both sides of the magnet.

In a third aspect of the present invention, said sleeve, the magnet andthe rotor stacks provided on both sides thereof described in the firstaspect are solidified by being molded with a resin in a unit.

By thus forming the rotor, the cutting process of the outer diameter ofthe rotor (rotor assembly) which is not mounted on the rotary shaft yetbecomes possible.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a sectional view of a rotor according to one embodiment of thepresent invention.

FIG. 2 is a sectional view showing the time when the outer diameter ofwhat is shown in FIG. 1 is cut.

FIG. 3 is a sectional view of a stepping motor to be applied by thepresent invention.

FIG. 4 shows a stator core of what is shown in FIG. 3.

FIG. 5 is a perspective view of what is shown in FIG. 4.

FIG. 6 is a sectional view of a rotor of the conventional steppingmotor.

FIG. 7 is a sectional view showing the time when the outer diameter ofthe rotor of the conventional stepping motor is cut.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

Hereinafter, an embodiment of the present invention will be describedbased on FIG. 1. In the present invention, the holes 3 b, 4 b and 5 bpierced at the center of the magnet 3, the rotor stacks 4 and 5respectively are adapted to become lager in diameter compared with theprevious mentioned holes 3 a, 4 a and 5 a respectively, in which thenon-magnetic sleeve 15 having the length to the extent where both endsthereof are projected out of the rotor stacks axially is pressed inwhile interposing therebetween.

The portions except the rotary shaft 2 of the rotor 6, thus after thesleeve 15 is inserted, is formed by being molded with a resin in a unit.In order to press in the sleeve 15, the outer diameter dimension isadapted to be approximately identical with the above holes 3 a, 4 a and5 a, the dimension of hole 15a keeps a concentricity in a high precisionwith the outer diameter.

As shown in FIG. 2, in the hole 15 a thus constructed, a center holemaintaining apparatus 13 of an outer diameter cutting apparatus isinserted to set the concentricity in a high precision, and a grindingstone 14 for use of outer diameter cutting is gotten in touch with theouter circumference of the rotor 6 and the outer circumference is cut insuch a manner as it becomes a given dimension. After finishing thecutting, a rotary shaft 2 having the length suitable for that use ispressed in the hole 15 a and glued to form the rotor 6.

Thus, according to this structure, regardless of the length of therotary shaft 2, the outer diameter can be worked by cutting.

Since the present invention is a stepping motor thus structured,according to a first aspect of the invention, and the outer diametercutting work of the rotor which is not assembled with the rotary shaftcan be carried out, it is greatly effective in the light of a processcontrol. And, since, regardless of the length of the rotary shaft thecutting work of the outer diameter can be carried out, the kind of themold which is used for manufacturing the rotor can be reduced.

Further, since the non-magnetic sleeve prevents the magnetic flux fromleaking, as the material to be used for the rotary shaft, it is notlimited to a non-magnetic material but a magnetic material also can beused. Further, in the 2nd aspect of the present invention, since thelength of the sleeve is set in such a manner as it is projected in theaxial direction from the rotor stacks disposed on both sides of themagnet, when the length of the sleeve is prolonged as long as possible,a decrease of the mechanical strength of the rotor due to theminiaturization of the stepping motor can be supplemented.

Further, in the third aspect of the present invention, since the sleeve,the magnet provided on its outer circumference and the rotor stacks aresolidified by molding of a resin in a unit, at the time of cutting workof the diameter a displacement between the rotor stacks and the magnetis not generated to ease the cutting work.

What is claimed is:
 1. A process for producing a rotor assembly of astepping motor, comprising the ordered steps of: (a) clamping both sidesof a cylindrical magnet magnetized in axial direction with a pair ofrotor stacks provided with pole teeth on outer circumferences thereofand formed by laminating electrically insulated annular magnetic plates;(b) disposing a cylindrical non-magnetic sleeve within the magnet andthe rotor stacks by press fitting the sleeve; (c) solidifying themagnet, the rotor stacks and the sleeve with a resin in a unitarymanner; (d) directly inserting a center hole maintaining apparatus of anouter diameter grinding machine into both ends of the sleeve; (e)grinding the outer circumferences of the rotor stacks with a grindingstone of the outer diameter grinding apparatus until the outercircumferences of the rotor stacks become a predetermined outerdiameter; (f) press fitting a rotary shaft having a predetermined lengthby each motor into the sleeve; and (g) gluing the rotary shaft to thesleeve.
 2. The process according to claim 1, wherein the sleeve projectsaxially from both sides of the rotor stacks.